Microstructured thermosensor

ABSTRACT

A micropatterned thermosensor, e.g., an infrared sensor, includes a supporting body and at least one thermocouple arranged thereon. The thermocouple also has a first material and a second material, which together form, at least in a pointwise manner, at least one thermal contact. Furthermore, it is provided that the first and/or the second material are configured at least regionally in the form of a meander-shaped or undulating-type circuit trace and extend on the supporting body. In addition, a micropatterned thermosensor having such patterned circuit traces, in which the first material is platinum or aluminum, and the second material is doped or undoped polysilicon-germanium.

FIELD OF THE INVENTION

The present invention relates to a micropatterned thermosensor, e.g., aninfrared sensor.

BACKGROUND INFORMATION

Conventional infrared sensors, such as they are used in safetyengineering, plant technology or in the household appliance industry,measure the temperature of a body from the infrared radiation it emits.Basically, the distinction is made among so-called pyroelectric,bolometric as well as thermoelectric sensors.

It is conventional to produce thermoelectric sensors using thin-filmtechnology, for instance on polyimide foil. Furthermore, micropatternedthermosensors based on silicon technology are also generallyconventional.

German Published Patent Application No. 199 32 308 describesmanufacturing a thermosensor in the form of a thermal column that ispositioned on an at least substantially self-supporting membrane, thethermal contacts of this thermal column being designed to alternate as“hot” and “cold” thermal contacts and being connected to a supportingbody by appropriate contact columns, as well as being electricallycontrollable via these contact columns. German Published PatentApplication No. 199 32 308 also describes implementing the thermocouplesrunning on the surface of the substantially self-supporting membrane inthe form of circuit traces, which are alternately produced from a firstand a second material, so that thermal contacts are created in theregion where these two materials come in contact. The first material, inthis case, is aluminum, while polysilicon is used as a second material.

German Published Patent Application No. 100 09 593 describes designing amicropatterned thermosensor in the form of an infrared-sensor, forinstance, using sacrificial layer technology or some other etchingtechnology, by first creating a thin, self-supporting membrane on asilicon substrate, which is thermally decoupled from a subjacentsubstrate due to its low thermal conductivity, so that in response toincident infrared radiation, the membrane is warmed more than thesubstrate. A plurality of micropatterned sensor elements orthermocouples are then situated on the membrane, whichthermoelectrically convert a temperature difference between the centerof the membrane and the substrate into an electrical signal that isproportional thereto. In accordance with German Published PatentApplication No. 100 09 593, the material combinationsplatinum/polysilicon, aluminum/polysilicon or p-type dopedpolysilicon/n-type doped silicon are used for the thermocouples createdon the self-supporting membrane in the form of circuit traces. Thematerial combination polysilicon/aluminum, which is used primarily inbulk micro-technology, may have the advantage of being CMOS-compatible.

It is conventional that gold, antimony, bismuth and lead tellurides mayalso be used as materials for thermocouples, with gold also beingsuitable for bulk micromechanics.

It is an object of the present invention to provide a micropatternedthermosensor having improved sensitivity and stability at highertemperatures than conventional micropatterned thermal sensors.

SUMMARY

Due to at least one of the patterning of the printed circuit traces onthe supporting body and/or the particular choice of materials for thethermocouple, the micropatterned thermosensor according to the presentinvention may have the advantage of achieving a higher temperaturesensitivity, without this entailing significant changes in the currentmanufacturing methods for micropatterned thermosensors. Specifically,according to the present invention, it is merely the layout of theproduced printed circuit traces of the thermocouples and/or the materialused for depositing these printed circuit traces that are/is modified.

Through the choice of materials for the thermocouple, i.e., the materialcombination platinum or aluminum with doped or undopedpolysilicon-germanium, the produced micropatterned thermosensor may havea markedly increased temperature stability compared to conventionalthermosensors using aluminum with polysilicon, for instance, as materialfor the thermocouple.

Through the choice of materials for the thermocouple, migration effectsoccurring at temperatures above 200° C. may also be avoided, and thusstability problems in the produced thermosensor, as often observed insensors where polysilicon and aluminum are used as material for thethermocouple.

Furthermore, the aluminum widely used in conventional methods is anexcellent thermal heat conductor, which means that the thermocouplemanufactured therefrom has a relatively low thermoelectriceffectiveness, whereas platinum, on the one hand, may be used attemperatures of up to 400° C. and, on the other hand, has a thermalconductivity that is lower by a factor of 3 compared to aluminum. Incontrast to polycrystalline silicon, polycrystalline, doped or undopedpolysilicon-germanium also has a thermal conductivity that is lower by afactor of 3 to 8 and, therefore, also results in a markedly increasedthermoelectric effectiveness of the produced thermocouple.

An especially high increase in sensitivity and an especially goodtemperature stability of the thermosensor may be achieved by acombination of the meander-shaped or undulating-type layout of themicropatterned circuit traces on the surface of the supporting body andthe mentioned special materials for the thermocouple.

Depending on the intended use of the micropatterned thermocouple, forinstance, as an infrared sensor, the mentioned materials for thethermocouple may be combined with one another, using p-type doped orn-type doped material for the semiconductor material.

Since a temperature difference between so-called “hot” and “cold”contacts may be thermoelectrically converted into a measurable electricvoltage in micropatterned thermosensors, the “cold” points either may bekept at a constant temperature, or this temperature may be known orreferenced relative to the temperature of the “hot” contact. Normally,for that purpose in conventional methods, so-called thermistors areintegrated in hybrid technology on the supporting body for thethermocouple, since the employed materials, aluminum and polysilicon,are often not sensitive enough to determine this reference temperature.

When using platinum as thermoelectric material, it may be possible tointegrate, or deposit, a high-precision, resistive temperature measuringelement on the silicon chip, or the supporting body supporting thethermocouple, during the same manufacturing step as that for thecorresponding printed circuit trace or conductor. This eliminates theneed for an additional thermistor.

Implementing the printed circuit traces in the form of meander-shaped,or undulating-type printed circuit traces extending on the supportingbody, may offer the further possibility of implementing only thoseprinted circuit traces having the lower internal resistance in the formof meanders, since increased noise voltage may result when a meander orundulating-type pattern is used in materials having a high electricalresistance.

The meander-shaped or undulating-type circuit traces may be implementedas extending side-by-side and also as overlapping or running one overanother, at least regionally, in which case they may then be separatedfrom one another in an electrically insulating manner by suitableinsulating layers of oxides, for instance. If sufficient surface area isavailable, it may be advantageous to configure the circuit tracesside-by-side.

It may be possible to also vary, or increase, the sensitivity of theresulting micropatterned thermosensor by varying the number ofundulations or meanders. In this context, one utilizes the fact that thethermal resistance of a printed circuit trace increases with length,that is, the thermal resistance of a printed circuit trace having ameander pattern is greater than that of one using a correspondingstraight-line pattern.

The invention is explained in greater detail in the followingdescription with reference to the drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 illustrates a single thermocouple created on the surface of asupporting body in the form of deposited printed circuit traces runningside-by-side.

FIG. 2 illustrates a plurality of thermal contacts arranged in the formof a thermo-chain.

FIG. 3 shows a cut-away portion of a cross section of the membranelayer.

DETAILED DESCRIPTION

In the example embodiment, the present invention is initially based onan infrared sensor, as is described in German Published PatentApplication No. 100 09 593. However, the infrared sensor it describes ismodified in two respects.

Specifically, as described in German Published Patent Application No.100 09 593, an at least substantially self-supporting membrane iscreated from a poorly heat-conducting material, such as an oxide, anitride or a combination of both materials, on a substrate materialhaving good heat-conducting properties, for instance, silicon. The atleast substantially self-supporting membrane, which may be used assupporting body 12 for a thermocouple 20 to be deposited thereon, may bemade of silicon dioxide, silicon nitride or of porous silicon.

A plurality of thermocouples 20 may be created on the surface of thissupporting body 12. They may be connected in series and arranged in across-pattern or star-pattern. As illustrated in FIG. 1, which onlyillustrates one of these thermocouples 20, a first material 13 may firstbe deposited on supporting body 12 in the form of a first,meander-patterned circuit trace 15, and a second material 14 may bedeposited in the form of a second circuit trace 16, which may be alsomeander-patterned. As illustrated in FIG. 1, first circuit trace 15 andsecond circuit trace 16 extend at least substantially parallel to oneanother.

First material 13 and second material 14 may come in contact with oneanother in the region of a first thermal contact 10 and a second thermalcontact 11, and that further conductors 17 leading to thermocouple 20may be provided, which may be developed and deposited in an analogousfashion to second printed circuit trace 16, so that thermocouple 20 maybe electrically interconnected to, or controlled by, electroniccomponents via these conductors 17, in a conventional manner.

Also illustrated in FIG. 1 is that first thermal contact 10 may beexposed to a first temperature T₁, and second thermal contact 11 may beexposed to a second temperature T₂. In this context, temperature T₂ isthe actual temperature to be detected or measured by micropatternedthermosensor 5, while temperature T₁ is being kept at leastapproximately constant, or may alternatively be determined by anadditional measuring device. In this respect, temperature T₁ of firstthermal contact 10 (“cold” thermal contact) serves as a referencetemperature for temperature T₂ of second thermal contact 11 (“hot”thermal contact), which may be measured.

The width of circuit traces 14, 15 and conductors 17 may be between 20nm and 200 μm, e.g., between 1 μm and 20 μm. Their thickness may bebetween 10 nm and 10 μm, e.g., between 100 nm and 2 μm. The first orsecond printed circuit traces 15, 16, respectively, as well as theirmeander patterning, and conductors 17 may be fabricated in aconventional manner by sputter depositing or vapor depositing of therespective materials 13, 14, for instance through PECVD (“PhysicallyEnhanced Chemical Vapor Deposition”) or LPCVD (“Low Pressure ChemicalVapor Deposition”).

First material 13 in the example embodiment may be n-type dopedpolysilicon-germanium, having a thermal conductivity of 3 to 8 w/km.Second material 14 in the example embodiment may be platinum, having athermal conductivity of 70 w/km. Furthermore, analogously to secondcircuit trace 16, conductor 17 may be in each case developed in the formof a platinum circuit trace, resulting in two thermocontacts 10, 11,both formed from the material combination ofplatinum/polysilicon-germanium.

Alternatively to the example embodiment illustrated in FIG. 1, firstcircuit trace 14 and second circuit trace 15 may also extend over oneanother, regionally or entirely, and be electrically insulated from oneanother, except for thermal contacts 10, 11. In this case, theelectrical insulation may be assured by an oxidic, electricallyinsulating intermediate layer between circuit traces 15, 16.

Furthermore, instead of two thermal contacts 10, 11, a plurality ofthermal contacts may also be provided, which may be configured in themanner of a thermal chain or a thermal column. In this case, at leasttwo of the thermal contacts are exposed to different temperatures.

In a further example embodiment of the present invention, a part of afurther measuring device may be additionally created, or integrated, onsupporting body 12 in the form of a circuit trace, in order to determinefirst temperature T₁. This eliminates the need to integrate the usualthermistor on the surface of supporting body 12 in the area of firstthermal contact 10.

The measuring device may be realized by providing an additionalreference circuit trace made from platinum in one vicinity of firstthermal contact 10 as sensitive component of this measuring device, thismeasuring device also being interconnected via appropriate conductors togenerally conventional evaluation devices for determining atemperature-dependent electrical resistance of this reference circuittrace. This reference circuit trace may be designed, for instance,analogously to conductor 17 or second circuit board conductor 16.

Alternatively, however, the measuring device may also be realized byusing one segment of second circuit trace 16 or of conductors 17 asreference circuit trace and may be interconnected to appropriateevaluating arrangements for determining the temperature-dependent,electrical resistance of this part of the circuit trace.

This possibility of integrating an additional reference circuit trace onsupporting body 12, or the possibility of using a part of second circuittrace 16 or of conductor 17 as reference circuit trace on supportingbody 12 to measure or monitor temperature T₁, is the result ofplatinum's suitability for high-precision, resistive temperaturemeasuring.

With respect to further details regarding the design of thermocouple 20and the function and the further design of thermocouple 5 according toFIG. 1, reference is made to German Published Patent Application No. 10009 593, which describes this thermosensor 5, apart from the specificlayout of circuit traces 15, 16 of thermocouple 20 and the choice ofmaterials for thermocouple 20, in the form of an infrared sensor.

FIG. 2 shows a plurality of the thermal contacts (10, 11, 24), which arearranged in the form of a thermo-chain, at least (10) and (11) beingsubjected to different temperatures. The self-supporting membrane (22)acts as insulator between the two materials at the indicated locations,since it is made of an oxide, a nitride or a combination of bothmaterials. An additional measuring device (6) having an evaluation means(28) is used for temperature measurement T1.

FIG. 3 shows a cut-away portion of a cross section of the membrane layerin which the two circuit traces (15, 16) run on top of one another.Except for the thermojunctions, they are electrically insulated from oneanother by an oxide layer (30).

1. A micropatterned thermosensor, comprising: a supporting body; and atleast one thermocouple located on the supporting body, the thermocoupleincluding a first material and a second material which form at least ina point-wise manner, at least one thermal contact with each other, atleast one of the first material and the second material at leastregionally configured in the form of one of a meander-shaped and anundulating circuit trace and arranged on the supporting body; whereinthe first material and the second material extend one of substantiallyside-by-side in the form of circuit traces, the first material and thesecond material electrically insulated from one another with theexception of thermal contacts, and extend over one another at leastregionally in the form of circuit traces, the first material and thesecond material electrically insulated from one another with theexception of thermal contacts; wherein the thermocouple includes aplurality of thermal contacts configured as one of a thermal chain and athermal column, at least two of the thermal contacts to differenttemperatures; and wherein a first one of the thermal contacts is exposedto a first temperature, the first temperature kept one of constant andat least approximately constant, and a second one of the thermalcontacts is exposed to a second temperature, the second temperature tobe one of detected and measured, the thermosensor further comprising anadditional measuring device configured to detect the first temperature.2. The micro patterned thermosensor according to claim 1, wherein themicropatterned thermosensor is an infrared sensor.
 3. The micropatternedthermosensor according to claim 1, wherein at least one of the first andthe second material includes a material having low thermal conductivity.4. The micropatterned thermosensor according to claim 1, wherein themeasuring device includes one of includes a part of one of the circuittraces, arranged in the vicinity of one of the first thermal contact,and of a conductor, and a reference circuit trace as a sensitivecomponent, arranged in a vicinity of the first thermal contact, andwherein the measuring device includes an evaluation arrangementconfigured to determine a temperature dependent, electrical resistanceof one of the part of the trace, the conductor and the reference circuittrace.
 5. The micropatterned thermosensor according to claim 4, whereinone of the part of the circuit trace, the conductor and the referencecircuit trace includes a platinum circuit trace.
 6. The micropatternedthermosensor according to claim 1, wherein the first and the secondmaterial includes at least one of platinum, gold, lead tellurides,aluminum, titanium, polysilicon, doped polysilicon, undopedpolysilicon-germanium, and doped polysilicon-germanium.
 7. Themicropatterned thermosensor according to claim 6, wherein the firstmaterial includes one of doped and undoped polysilicon-germanium and thesecond material includes platinum.
 8. A micropatterned thermosensor,comprising: a supporting body; and at least one thermocouple located onthe supporting body, the thermocouple including a first material and asecond material, which form at least in a point-wise manner at least onethermal contact with each other, the second material including platinumand the first material including one of doped and undopedpolysilicon-germanium; wherein the first material and the secondmaterial extend one of substantially side-by-side in the form of circuittraces, the first material and the second material electricallyinsulated from one another with the exception of thermal contacts, andextend over one another at least regionally in the form of circuittraces, the first material and the second material electricallyinsulated from one another with the exception of thermal contacts;wherein the thermocouple includes a plurality of thermal contactsconfigured as one of a thermal chain and a thermal column, at least twoof the thermal contacts exposed to different temperatures; and wherein afirst one of the thermal contacts is exposed to a first temperature, thefirst temperature kept one of constant and at least approximatelyconstant, and a second one of the thermal contacts is exposed to asecond temperature, the second temperature to be one of detected andmeasured, the thermosensor further comprising an additional measuringdevice configured to detect the first temperature.
 9. The micropatternedthermosensor according to claim 8, wherein the micropatternedthermosensor is an infrared sensor.
 10. The micropatterned thermosensoraccording to claim 8, wherein at least one of the first material and thesecond material is configured at least regionally in a form of one of ameander-shaped and an undulating circuit trace and extends on thesupporting body.
 11. The micropatterned thermosensor according to claim8, wherein the thermocouple includes a plurality of contacts configuredas one of a thermal chain and a thermal column, at least two thermalcontacts exposed to different temperatures.